Power saving in liquid crystal display devices and other display devices is an ongoing challenge. Toward this end, Patent Document 1, for example, discloses a display device driving method in which a refreshing period during which a display image is refreshed by scanning gate lines that serve as scanning signal lines of the liquid crystal display device is followed by a non-refreshing period during which refreshing is stopped by bringing all of the gate lines into a non-scanning state. In this intermission period, it is possible not to supply signals such as control signals to, e.g., a gate driver which serves as a scanning signal line drive circuit and/or a source driver which serves as a data signal line drive circuit. This makes it possible to stop operation of the gate driver and/or the source driver, and therefore to reduce power consumption. The driving method in which a refreshing period is followed by a non-refreshing period (intermission period) as exemplified in Patent Document 1 is called “intermission driving” for example. The intermission driving is also called “low-frequency driving” or “intermittent driving”. Intermission driving as described above is suitable for displaying a still image. Inventions related to intermission driving are disclosed in Patent Document 2 and other publications as well as Patent Document 1.
In a display device in which intermission driving as described above is performed, display image is not refreshed for every frame period when there is no change in the image which is to be displayed. However, display image must be refreshed for every predetermined period which is longer than one frame period. If the display device is provided with a frame buffer which holds display image data to be used for the refreshing, it is possible to carry out the refreshing within the display device by internal operation. In many cases, however, the frame buffer is not provided within the display device for the sake of cost reduction, and in such a case, a frame buffer is provided in a main body of an electronic appliance that has the display device as a component. In this case, there are two conventional methods for transferring the image data to the display device for the refreshing purpose: In the following description, the main body to which the display device is connected in the electronic appliance (portable terminal for example) will be called “host”, and it is assumed that the display device and a data processing device which serves as the host are connected with each other and capable of sending/receiving data therebetween.
In the first method, display image refreshing timing management is made within the display device: As shown in FIG. 17, in the electronic appliance which includes the display device, a signal for requesting transfer of image data for the purpose of refreshing (hereinafter called “REQUEST signal”) is sent from the display device to the host. Upon receiving the REQUEST signal, the host reads out the image data which is stored in the frame buffer provided in the host, and sends the data to the display device. Upon receiving this image data, the display device drives its display section based on the data, thereby refreshing the display image.
In the second method, a frame buffer for storing image data to be displayed in the display device is provided on the host side, and the host determines whether the display device is in its intermission state or normal state, based on whether or not the image data in the frame buffer has been updated. If a result of determination indicates that the display device is in the intermission state, the host sends the image data stored in the frame buffer to the display device periodically as shown in FIG. 18 at a predetermined time interval while the display device is in its intermission state.